[dm-devel] [RFC PATCH v2 0/2] add simple copy support

[Johannes Thumshirn]

On 08/12/2020 14:13, Javier González wrote:
> On 08.12.2020 12:37, Johannes Thumshirn wrote:
>> On 08/12/2020 13:22, Javier González wrote:
>>> Good idea. Are you thinking of a sysfs entry to select the backend?
>>
>> Not sure on this one, initially I thought of a sysfs file, but then
>> how would you do it. One "global" sysfs entry is probably a bad idea.
>> Having one per block device to select native vs emulation maybe? And
>> a good way to benchmark.
> 
> I was thinking a per block device to target the use case where a certain
> implementation / workload is better one way or the other.

Yes something along those lines.

>>
>> The other idea would be a benchmark loop on boot like the raid library
>> does.
>>
>> Then on the other hand, there might be workloads that run faster with
>> the emulation and some that run faster with the hardware acceleration.
>>
>> I think these points are the reason the last attempts got stuck.
> 
> Yes. I believe that any benchmark we run would be biased in a certain
> way. If we can move forward with a sysfs entry and default to legacy
> path, we would not alter current behavior and enable NVMe copy offload
> (for now) for those that want to use it. We can then build on top of it.
> 
> Does this sound like a reasonable approach?
> 

Yes this sounds like a reasonable approach to me.